Department of Biology

Education

Ph.D., University of California, Santa Cruz, 2002
B.A., Earlham College, 1994

Research Description

My research interests are in community ecology and species interactions, particularly between plants and animals.  My current research is primarily focused on topics of local conservation importance in Indiana forests.  I combine field observations and experiments, greenhouse experiments, and computational and GIS modeling to try to understand complex species interactions and their consequences on communities.

Ecological Effects of Deer on Forests
White-tailed deer are very abundant in many Midwestern forests.  Because they lack any natural predators, they can reach high population densities and can dramatically effect the plants and other aspects of forest communities.  We are exploring the hypothesis that deer act as a keystone species in forests where they are highly abundant.  We have established several deer exclosures at three IU Research and Teaching Preserve properties.  We are comparing the communities inside and outside these fences, including herbaceous and woody plants, nutrient dynamics, arbuscular mycchorizae (AMF) communities, and soil conditions.  We are also examining how these effects scale up in the communities by testing usage of the fenced and unfenced areas by mice, salamanders, and ticks.  Our results to date reveal a very strong effect of deer altering the forest community.

Spread of an Aggressive Invader in Forest Understories
Invasive species are one of the most significant environmental issues in many ecosystems. They can reduce biodiversity, degrade habitat, and transform ecosystems to less robust and less desirable states.  Land managers regularly try to control invasive species but they do not have sufficient time or resources to eliminate all of them.  Therefore, they try to target new invasives and control them while populations are still small. 

We have mapped the spread of a very fast-spreading invasive grass, Japanese stiltgrass (Microstegium vimineum), that is invading eastern U.S. forests.  We used GIS to map occurrences of this plant across a dozen field sites in southern Indiana that were either undisturbed, naturally disturbed by storms or flooding, or disturbed by timber harvesting.  We compared the rate of spread, particularly via corridors such as roads, trails, and waterways, at these sites.  We are using these data to develop a spatial predictive model of spread of this invasive species.  We hope this model will be useful to land managers and that it may be extended for other invasive species that spread via corridors. 

Effects of Periodical cicada oviposition
Periodical cicadas represent one of the highest densities of organisms in nature.  They live underground for 13 or 17 years (depending on the geographic region) and then emerge en masse for 3-4 weeks to mate and lay eggs.  The eggs then hatch and return to the soil where they feed on xylem from tree roots until it is time for them to emerge.  During their emergences, they lay eggs on the underside of tree branches, causing many oviposition scars that kill small branches of trees.  In collaboration with Keith Clay (IU Biology), we measured the effects of oviposition on tree growth and survival.  In a very large study of netted and unnetted trees during the 2004 emergence of Brood X in Indiana, we recorded high levels of ovipositon.  However, over the next several years, we found no difference in tree growth due to the oviposition.  Trees were able to compensate for the damage and had no long-term effects. 

Interactions between plant chemistry and insect herbivores
Most plants defend themselves with a wide variety of chemical and mechanical defenses.  I examined how these defenses affect the behavior of insect herbivores and, in turn, how the herbivores affect the plants defenses.  Using wild radish (Raphanus sativus) as a model system, did chemical analyses of the chemical defenses within the plants at a small scale.  I found high levels of spatial variation within individual leaves and this variation, as well as the mean level of defense, increased in response to feeding by herbivores.  I conducted feeding trials with caterpillars on live plants and leaf disks from plants and used the data from both the plant chemistry and the caterpillar growth and behavior to parameterize a dynamic state-variable model that predicted the interactions between herbivore behavior and plant chemistry.  This research reveals the dynamic two-way interaction between plants and their herbivores and gives insight into effective plant defense strategies.

Synergistic Activities

I am interested in applying the results of my research to local environmental issues and communicating ecological knowledge to the public.  I have been a member of the City of Bloomington\'s Parks Department\'s Environmental Resources Advisory Council (ERAC) since 2008 and currently serve as chair.  

I have also been involved with the Griffy Lake Management Plan steering committee and have presented research to the Bloomington Deer Task Force on several occasions. 

I work with outreach education through the IU Research and Teaching Preserve teaching environmental and ecological science to all ages from preschool through adults.

Select Publications

Shelton, A.L. In Review. Seasonality is Not Important for Management of Japanese Stiltgrass by Mowing. Invasive Plant Science and Management.

Clay, K., J.A. Rudgers, A.L. Shelton. 2010. Tall Fescue, Endophyte Infection and Vegetation Change: A 10-Year Experiment. Proceedings of the 2010 International Symposium on Fungal Endophytes of Grasses.

Clay, K., A.L. Shelton, C. Winkle. 2009. Differential susceptibility of tree species to oviposition by periodical cicadas. Ecological Entomology 24: 277-286.

Clay, K., A.L. Shelton, C. Winkle. 2009. Effects of oviposition by periodical cicadas on tree growth. Canadian Journal of Forest Research 39: 1688-1697.

Shelton, A.L. 2005. Within-plant variation in glucosinolate concentrations of Raphanus sativus across multiple scales. Journal of Chemical Ecology 31(8): 1711-1732.

Shelton, A.L. 2004. Variation in chemical defenses of plants may improve the effectiveness of plant defence. Evolutionary Ecology Research 6: 709-726.

Shelton, A.L. 2000. Variable chemical defenses in plants and their effects on herbivore behavior. Evolutionary Ecology Research 2: 231-249.

Shelton, A.L. and R.S. Inouye. 1995. Effect of browsing by deer on the growth and reproductive success of Lactuca canadensis (Asteraceae) in old fields in Minnesota. American Midland Naturalist 134(2): 332-339.

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